1. Field of the Invention
This invention relates to an improved environment system for sealed hard disk assemblies, and more particularly to a system that extends the operating life of the hard disk assembly when subject to high operating temperatures.
2. Description of the Prior Art
FIG. 1 schematically illustrates a commercially available sealed, hard disk drive and its environment control enclosure that makes the disk drive suitable for use in rugged applications where it is subject to high temperature and mechanical shock and/or vibration. One such sealed hard disk and environment control enclosure is available from Miltope Corporation and referred to by Miltope as the LPC Series of rugged high capacity, low profile, shock and vibration resistant disk drives employing sealed, disk drive cartridges. These products are ruggedized for operation in severe field environment where extremes of temperature, shock, vibration, humidity and air pressure are common. They are designed for "on-the-move" operation in tracked and wheeled vehicles, as well as airborne and shipboard applications. As illustrated in FIG. 1, this prior art disk drive includes a commercially available sealed hard disk drive 10, such as the sealed hard disk drive available from Toshiba, IBM Corp., Seagate and others. Such hard disk drives include a disk housing 12, which is sealed except for a very small opening 14 that allows a small amount of gas sealed in the housing 12 to egress and ingress during disk start up and shut down respectively. A hard disk 16 within the housing 12 rides on a spindle 17 driven by a motor 18, both of which are also located within the housing 12. A flying head 20 is servo positioned over a desired track on the disk 16 in order to read from and write data onto the disk. The housing 12 is supported in a sealed environmental housing 22 by resilient mounts 24, i.e. device to mechanically isolate rapid acceleration due to shock or vibration, for example, of the environmental housing 22 from the disk housing 12. The environmental housing 22 is an air tight aluminum housing filled with an inert gas or, if desired, with dry or low humidity air. This sealed aluminum housing 22 can also house a control electronics module 30. An embedded closed loop servo system compensates for temperature variation, ensuring reliable head positioning. An air tight connector 32 provides a signal and power interface between the components inside the sealed environmental housing 22 and connections (not shown) outside of the housing. As will be appreciated by those skilled in the art, hard disk drives of the type shown schematically in FIG. 1, store multi-gigabytes of data on a 2.5 inch or 3.5 inch disk, with the environmental housing 22 having a foot print of approximately 5 inches by 8 inches by 1.5 inches deep for a 3.5 inch disk, or appropriately smaller for a 2.5 inch or smaller hard drive. The expected mean time between failures is normally in excess of 100,000 hours in a normal environment application.
While quite satisfactory in normal office type operation, the hard disk drive systems of the type shown in FIG. 1 have experienced a significant increase in failures when operating at very high temperatures.